Hiv-1 subtype isolate regulatory/accessory genes, and modifications and derivatives thereof

ABSTRACT

The invention describes HIV-1 subtype isolate regulatory/accessory genes, and modifications and derivatives thereof. The genes which are described are the tat, nef and rev genes. Consensus amino acid sequences are also disclosed. The invention also relates to a vaccine including two or more of the nucleotide sequences, and nucleotide sequences from the pol and/or gag genes of HIV-1.

BACKGROUND TO THE INVENTION

THIS invention relates to a process for the selection of HIV-1 subtype (clade) C isolate regulatory/accessory genes, selected HIV-1 subtype C isolate regulatory/accessory genes and modifications and derivatives thereof for use in prophylactic and therapeutic vaccines to produce proteins and polypeptides for the purpose of eliciting protection against HIV infection or disease.

The disease acquired immunodeficiency syndrome (AIDS) is caused by human immunodeficiency virus (HIV). Over 34 million people worldwide are thought to be living with HIV/AIDS, with over 95% of infected people living in developing countries (UNAIDS, 1999). It is estimated that 24.5 million infected people reside in sub-Saharan Africa and that South Africa currently has one of the world's fastest growing HIV-1 epidemics. At the end of 2000, over 24% of pregnant women attending government antenatal clinics in South Africa were HIV positive (Department of Health, 2001). A preventative vaccine is considered to be the only feasible way to control this epidemic in the long term.

HIV shows remarkable genetic diversity that has confounded the development of a vaccine. The molecular basis of variation resides in the viral enzyme reverse transcriptase which not only introduces an error every round of replication, but also promotes recombination between viral RNAs. Based on phylogenetic analysis of sequences, HIV has been classified into a number of groups: the M (major group) which comprises subtypes A to H and K, the O (outlier group) and the N (non-M, non-O group). Recently recombinant viruses have been more frequently identified and there are a number which have spread significantly and established epidemics (circulating recombinant forms or CRF) such as subtype A/G recombinant in West Africa, and CRF A/E recombinant in Thailand (Robertson et at., 2000).

Subtype C predominates in the Southern African region which includes Botswana, Zimbabwe, Zambia, Malawi, Mozambique and South Africa. In addition, increasing numbers of subtype C infections are being detected in the Southern region of Tanzania. This subtype also predominates in Ethiopia and India and is becoming more important in China.

A possible further obstacle to vaccine development is that the biological properties of HIV change as disease progresses. HIV requires two receptors to infect cells, the CD4 and co-receptors of which CCR5 and CXCR4 are the major co-receptors used by HIV-1 strains. The most commonly transmitted phenotype is non-syncytium inducing (NSI), macrophage-tropic viruses that utilise the CCR5 co-receptor for entry (R5 viruses). Langerhans cells in the mucosa are thought to selectively pick up R5 variants at the portal of entry and transport them to the lymph nodes where they undergo replication and expansion. As the infection progresses, viruses evolve that have increased replicative capacity and the ability to grow in T cell lines. These syncytium-inducing (SI) T-tropic viruses use CXCR4 in conjunction with or in preference to CCR5, and in some cases also use other minor co-receptors (Connor et al., 1997, Richman & Bozzette, 1994). However HIV-1 subtype C viruses appear to be unusual in that they do not readily undergo this phenotypic switch, as R5 viruses are also predominant in patients with advanced AIDS (Bjorndal et al., 1999, Peeters et al., 1999, Tscherning et al., 1998, Scarlatti et al., 1997).

An HIV vaccine alms to elicit both a CD8+ cytotoxic T lymphocyte (CTL) immune response as well as a neutralizing antibody response. Many current vaccine approaches have primarily focused on inducing a CTL response. It is thought that the CTL response may be more important as it is associated with the initial control of viral replication after infection, as well as control of replication during disease, and is inversely correlated with disease progression (Koup et al., 1994, Ogg et al., 1999 Schmitz et al., 1999). The importance of CTL in protecting individuals from infection is demonstrated by their presence in highly exposed seronegative individuals, for example certain sex-workers in Kenya (Rowland-Jones et al.,1998).

Knowledge of genetic diversity is highly relevant to the design of vaccines aiming at eliciting a cytotoxic T-lymphocyte (CTL) response. There are many CTL epitopes in common between viruses (HIV Molecular Immunology Database, 1998). In addition, several studies have now shown that there is a cross-reactive CTL response: individuals vaccinated with a subtype B-based vaccine could lyse autologous targets infected with a diverse group of isolates (Ferrari et al., 1997); and CTLs from non-B infected individuals could lyse subtype B-primed targets (Betts et al. 1997; Durali et al, 1998). A comparison of CTL epitopes in the HIV-1 sequence database indicated that there is a greater conservation of cytotoxic T epitopes within a subtype compared to between subtypes and that there will be a greater chance of a CTL response if the challenge virus is the same subtype as the vaccine strain.

It is thought that the regulatory genes of HIV are extremely important in eliciting an Immune response. Tat, Rev and Nef are all expressed early in the infectious cycle and would thus provide targets for cytotoxic T lymphocytes (CTLs) early in infection, possibly allowing virus infected cells to be destroyed before the virus can spread (Klotman et. al., 1991; Addo et. al., 2001). In addition, there is promising data showing that the Tat protein elicits an effective immune response in HIV-infected, asymptomatic people (Calarota et al., 1999; Calarota et. al., 2001). It has recently been reported that the Tat protein is one of the first to undergo escape from CTL in infected macaques (Allen et. al., 2000). This indicates that there is immune pressure on tat and that there is an early response to the Tat protein.

Viral strains used in the design of a vaccine need to be shown by genotypic analysis to be representative of the circulating strains and not an unusual or outlier strain. In addition, it is important that a vaccine strain also has the phenotype of a recently transmitted virus, which is NSI and uses the CCR5 co-receptor.

DEFINITIONS

In the specification which follows, certain terms are intended to have the following meanings:

-   “wild-type” means the naturally occurring HIV codon bias of the     virus isolate; -   “codon optimised” means the resynthesis of the gene using a human     codon bias instead of the HIV codon bias; -   “truncated” means having the first ten amino acids removed from the     Nef protein to inactivate function whilst maintaining     immunogenicity; -   “shuffled” means the rearrangement of the Tat protein in order to     inactivate function whilst maintaining immunogenicity.

SUMMARY OF THE INVENTION

According to a first aspect of the invention a molecule is provided, the molecule having:

-   -   (i) the nucleotide sequence as set out in FIG. 1 (SEQ I.D. No.         1);     -   (ii) an RNA sequence corresponding to the nucleotide sequence         set out in FIG. 1 (SEQ I.D. No. 1);     -   (iii) a sequence which is at least 97% DNA similar to the         nucleotide sequence set out in FIG. 1 (SEQ I.D. No. 1) or an RNA         sequence corresponding to it, and which displays substantially         similar immunogenicity;     -   (iv) a sequence which is homologous to the nucleotide sequence         set out in Sequence I.D. No. 1 or an RNA sequence corresponding         to it; or     -   (v) a sequence which is a modification or derivative of the         sequence of any one of (i) to (iv).

The modified sequence is preferably that set out in either one of FIGS. 9 and 10, which are consensus sequences of Du422 and Du151 (SEQ I.D. Nos. 9 and 10).

According to another aspect of the invention a molecule is provided, the molecule having:

-   -   (i) the nucleotide sequence set out in FIG. 3 (SEQ I.D. No. 3);     -   (ii) an RNA sequence corresponding to the nucleotide sequence         set out in FIG. 3 (SEQ I.D. No. 3);     -   (iii) a sequence which is at least 97% DNA similar to the         nucleotide sequence set out in FIG. 3 (SEQ I.D. No. 3) or an RNA         sequence corresponding to it, and which displays substantially         similar immunogenicity;     -   (iv) a sequence which is homologous to the nucleotide sequence         set out in FIG. 3 (SEQ I.D. No. 3) or an RNA sequence         corresponding to it; or     -   (v) a sequence which is a modification or derivative of the         sequence of any one of (i) to (iv).

The modified sequence is preferably that set out in either one of FIGS. 9 and 10, which are consensus sequences of Du422 and Du151 (SEQ I.D. No. 9 and No. 10).

According to another aspect of the invention a molecule is provided, the molecule having:

-   -   (i) the nucleotide sequence set out in FIG. 5 (SEQ I.D. No. 5);     -   (ii) an RNA sequence corresponding to the nucleotide sequence         set out in FIG. 5 (SEQ I.D. No. 5);     -   (iii) a sequence which is at least 98% DNA similar to the         nucleotide sequence set out in FIG. 5 (SEQ I.D. No. 5) or an RNA         sequence corresponding to it, and which displays substantially         similar immunogenicity;     -   (iv) a sequence which is homologous to the nucleotide sequence         set out in FIG. 5 (SEQ I.D. No. 5) or an RNA sequence         corresponding to it; or     -   (v) a sequence which is a modification or derivative of the         sequence of any one of (i) to (iv).

The modified sequence is preferably that set out in either one of FIGS. 12 and 13 (SEQ I.D. Nos. 11 and 13).

According to another aspect of the invention a molecule is provided, the molecule having:

-   -   (i) the nucleotide sequence set out in FIG. 7 (SEQ I.D. No. 7);     -   (ii) an RNA sequence corresponding to the nucleotide sequence         set out in FIG. 7 (SEQ I.D. No. 7);     -   (iii) a sequence which is at least 96% DNA similar to the         nucleotide sequence set out in FIG. 7 (SEQ I.D. No. 7) or an RNA         sequence corresponding to it, and which displays substantially         similar immunogenicity;     -   (iv) a sequence which is homologous to the nucleotide sequence         set out in FIG. 7 (SEQ I.D. No. 7) or an RNA sequence         corresponding to it; or     -   (v) a sequence which is a modification or derivative of the         sequence of any one of (i) to (iv).

The modified sequence preferably has similar or the same modifications as those set out in either one of FIGS. 12 and 13 (SEQ I.D. Nos. 12 and 13) for the nef gene of the isolate Du151.

According to another aspect of the invention a molecule is provided, the molecule having:

-   -   (i) the nucleotide sequence set out in FIG. 15 (SEQ I.D. No.         15);     -   (ii) an RNA sequence corresponding to the nucleotide sequence         set out in FIG. 15 (SEQ I.D. No. 15);     -   (iii) a sequence which is at least 90% or greater DNA similar to         the nucleotide sequence set out in FIG. 15 (SEQ I.D. No. 15) or         an RNA sequence corresponding to it, and which displays         substantially similar immunogenicity;     -   (iv) a sequence which is homologous to the nucleotide sequence         set out in FIG. 15 (SEQ I.D. No. 15) or an RNA sequence         corresponding to it; or     -   (v) a sequence which is a modification or derivative of the         sequence of any one of (i) to (iv).

According to another aspect of the invention a molecule is provided, the molecule having:

-   -   (i) the nucleotide sequence set out in FIG. 17 (SEQ I.D. No.         17);     -   (ii) an RNA sequence corresponding to the nucleotide sequence         set out in FIG. 17 (SEQ I.D. No. 17);     -   (iii) a sequence which is at least 90% DNA similar to the         nucleotide sequence set out in FIG. 17 (Sequence I.D. No. 17) or         an RNA sequence corresponding to it, and which displays         substantially similar immunogenicity;     -   (iv) a sequence which is homologous to the nucleotide sequence         set out in FIG. 17 (SEQ I.D. No. 17) or an RNA sequence         corresponding to it; or     -   (v) a sequence which is a modification or derivative of the         sequence of any one of (i) to (iv).

According to another aspect of the invention a polypeptide is provided, the polypeptide having:

-   -   (i) the amino acid sequence set out in FIG. 2 (SEQ I.D. No. 2);     -   (ii) a sequence which is at least 95% similar to the sequence of         FIG. 2 and which has substantially similar immunogenicity; or     -   (ii) a sequence which is a modification or derivative of the         amino acid sequence set out in FIG. 2 (SEQ I.D. No. 2).

The modified sequence is preferably that set out in FIG. 11, which is a consensus sequence of Du422 and Du151 (SEQ I.D. No. 11).

According to another aspect of the invention a polypeptide is provided, the polypeptide having:

-   -   (i) the amino acid sequence set out in FIG. 4 (SEQ I.D. No. 4);     -   (ii) a sequence which is at least 95% similar to the sequence of         FIG. 4 and which has substantially similar immunogenicity; or     -   (iii) a sequence which is a modification or derivative of the         amino acid sequence set out in FIG. 4 (SEQ I.D. No. 4).

The modified sequence is preferably that set out in FIG. 11 which is a consensus sequence of Du422 and Du151 (SEQ I.D. No. 11).

According to another aspect of the invention a polypeptide is provided, the polypeptide having:

-   -   (i) the amino acid sequence set out in FIG. 6 (SEQ I.D. No. 6);     -   (ii) a sequence which is at least 92% similar to the sequence of         FIG. 6 and which has substantially similar immunogenicity; or     -   (iii) a sequence which is a modification or derivative of the         amino acid sequence set out in FIG. 6 (SEQ I.D. No. 6).

The modified sequence is preferably that set out in FIG. 14 (SEQ I.D. No. 14).

According to another aspect of the invention a polypeptide is provided, the polypeptide having:

-   -   (i) the amino acid sequence set out in FIG. 8 (SEQ I.D. No. 8);     -   (ii) a sequence which is at least 95% similar to the sequence of         FIG. 8 and which has substantially similar immunogenicity; or     -   (iii) a sequence which is a modification or derivative of the         amino acid sequence set out in FIG. 8 (SEQ I.D. No. 8).

The modified sequence preferably has similar or the same modifications as those set out in FIG. 14 (SEQ I.D. No. 14) for the amino acid sequence of the nef gene of the isolate Du151.

According to another aspect of the invention a polypeptide is provided, the polypeptide having:

-   -   (i) the amino acid sequence set out in FIG. 16 (SEQ I.D. No.         16);     -   (ii) a sequence which is at least 90% similar to the sequence of         FIG. 16 and which has substantially similar immunogenicity; or     -   (iii) a sequence which is a modification or derivative of the         amino acid sequence set out in FIG. 16 (SEQ I.D. No. 16).

According to another aspect of the invention a consensus amino acid sequence for the tat gene of HIV-1 subtype C is the following: MEPVDPNLEPWNHPGSQPKTACNKCYCKHCSYHCLVCFQTKGLGISYGRKKRRQRRSAPP⁶⁰ (SEQ ID NO: 18) SSEDHQNLISKQPLPQTRGDPTGSEESKKKVESKTETDPFD¹⁰¹

According to another aspect of the invention a consensus amino acid sequence for the partial nef gene of HIV-1 subtype C is the following: MGGKWSKSSIVGWPAVRERIRRTEPAAEGVGAASQDLDKHGALTSSNTAHNNADCAWLQA⁶⁰ (SEQ ID No: 19) QEEEEEVGFPVRPQVPLRPMTYKGAFDLSFFLKEKGGLEGLIYSKKRQEILDLWVYHTQG¹²⁰ FFPDWQNYTPGPGVRYPLTFGWCFKLVPVDPREVEEANEGENNCLIHPMSQHGMEDEDRE¹⁸⁰ VLKWKFDSSLARRHMARELHPEYYKDC²⁰⁷

According to another aspect of the invention a consensus amino acid sequence for the partial rev gene of HIV-1 subtype C is the following: MAGRSGDSDEALLQAVRIIKILYQSNPYPKPEGTRQARKNRRRRWRARQRQIHSISERIL⁶⁰ (SEQ ID NO: 20) STCLGRPAEPVPLQLPPIERLHIDCSESSGTSGTQQSQQTTEGVGSP¹⁰⁷

According to a further aspect of the invention, there is provided the use of at least one of the sequences described above in the manufacture of a vaccine for use in the treatment or prevention of HIV infection. Preferably, at least two of the sequences are used in the vaccine.

According to a further aspect of the invention, there is provided a vaccine comprising at least two of the sequences described above.

According to a further aspect of the invention, there is provided a vaccine comprising at least portions of a gag gene sequence, a reverse transcriptase (pol) gene sequence; a shuffled tat gene sequence and a truncated nef gene sequence which have been ligated to form an in frame polygene designated grttnC (SEQ I.D. No: 30).

The vaccine may be for the treatment or prevention of HIV.

DESCRIPTION OF THE DRAWINGS

FIG. 1 (SEQ I.D. No 1) shows the nucleic acid sequence (cDNA) of the sequenced tat gene of the isolate Du422;

FIG. 2 (SEQ I.D. No 2) shows the amino acid sequence of the sequenced tat gene of the isolate Du422, derived from the nucleic acid sequence;

FIG. 3 (SEQ I.D. No 3) shows the nucleic acid sequence (cDNA) of the sequenced tat gene of the isolate Du151;

FIG. 4 (SEQ I.D. No 4) shows the amino acid sequence of the sequenced tat gene of the isolate Du151, derived from the nucleic acid sequence;

FIG. 5 (SEQ I.D. No 5) shows the nucleic acid sequence (cDNA) of the sequenced nef gene of the isolate Du151;

FIG. 6 (SEQ I.D. No 6) shows the amino acid sequence of the sequenced nef gene of the isolate Du151, derived from the nucleic acid sequence;

FIG. 7 (SEQ I.D. No 7) shows the nucleic acid sequence of the sequenced rev gene of the isolate Du422, derived from the nucleic acid sequence;

FIG. 8 (SEQ I.D. No 8) shows the amino acid sequence of the sequenced rev gene of the isolate Du422, derived from the nucleic acid sequence;

FIG. 9 (SEQ I.D. No 9) shows the nucleic acid sequence (DNA) of the wild-type, shuffled, sequenced tat gene of a consensus of the isolates Du422 and Du151;

FIG. 10 (SEQ I.D. No 10) shows the nucleic acid sequence (DNA) of the codon optimised, shuffled, sequenced tat gene of a consensus of the isolates Du422 and Du151 for the purposes of increased expression;

FIG. 11 (SEQ I.D. No 11) shows the amino acid sequence of the shuffled, sequenced Tat protein of a consensus of the isolates Du422 and Du151;

FIG. 12 (SEQ I.D. No 12) shows the nucleic acid sequence (DNA) of the wild-type, truncated, sequenced nef gene of the isolate Du151;

FIG. 13 (SEQ I.D. No 13) shows the nucleic acid sequence (DNA) of codon optimised, truncated, sequenced nef gene of the isolate Du151 for the purposes of increased expression;

FIG. 14 (SEQ I.D. No 14) shows the amino acid sequence of the truncated, sequenced Nef protein of the isolate Du151;

FIG. 15 (SEQ I.D. No 15) shows the nucleic acid sequence (DNA) of the wild-type polygene consisting of shuffled tat (SEQ I.D. No 9)—truncated nef (SEQ I.D. No 11) genes of the isolates Du422 and Du151;

FIG. 16 (SEQ I.D. No 16) shows the amino acid sequence of the sequenced shuffled Tat (SEQ I.D. No 10)—truncated Nef (SEQ I.D. No 12) polyprotein of the isolates Du422 and Du151; and

FIG. 17 (SEQ I.D. No 17) shows the nucleic acid sequence (DNA) of the sequenced polygene consisting of shuffled tat—truncated nef genes of the isolates Du422 and Du151 modified to reflect human codon usage for the purposes of increased expression.

FIG. 18 shows a schematic representation of the HIV-1 genome and illustrates the location of overlapping fragments that were sequenced having been generated by reverse transcriptase followed by polymerase chain reaction, in order to generate the South African consensus sequences;

FIG. 19 shows a phylogenetic tree of nucleic acid sequences of various HIV-1 subtype C isolates based on the sequences of the tat gene of the various isolates and includes a number of consensus sequences as well as the South African consensus sequence of the present invention and selected isolates, Du422 and Du151, of the present invention;

FIG. 20 shows a phylogenetic tree of nucleic acid sequences of various HIV-1 subtype C isolates based on the sequences of the nef gene of the various isolates and includes a number of consensus sequences as well as the South African consensus sequence of the present invention and a selected isolate, Du151, of the present invention;

FIG. 21 shows a phylogenetic tree of nucleic acid sequences of various HIV-1 subtype C isolates based on the sequences of the rev gene of the various isolates and includes a number of consensus sequences as well as the South African consensus sequence of the present invention and a selected isolate, Du422, of the present invention;

FIG. 22 shows how the sequences of the Tat proteins of each of a number of isolates varies from the South African consensus sequence for the tat gene which was developed according to the present invention;

FIG. 23 shows how the sequences of the Nef proteins of each of a number of isolates varies from the South African consensus sequence for the nef gene which was developed according to the present invention;

FIG. 24 shows how the sequences of the Rev proteins of each of a number of isolates varies from the South African consensus sequence for the rev gene which was developed according to the present invention;

FIG. 25 shows the phylogenetic tree of amino acid sequences of various HIV-1 subtype C isolates based on the sequences of the Tat protein of the various isolates and including a number of consensus sequences, as well as the South African consensus sequence of the present invention and selected isolates, Du422 and Du151, of the present invention;

FIG. 26 shows the phylogenetic tree of amino acid sequences of various HIV-1 subtype C isolates based on the sequences of the Nef protein of the various isolates and including a number of consensus sequences, as well as the South African consensus sequence of the present invention and selected isolates, Du422 and Du151, of the present invention;

FIG. 27 shows the phylogenetic tree of amino acid sequences of various HIV-1 subtype C isolates based on the sequences of the Tat protein of the various isolates and including a number of consensus sequences, as well as the South African consensus sequence of the present invention and selected isolates, Du422 and Du151, of the present invention;

FIG. 28 shows the percentage amino acid sequence identity of the sequenced Tat proteins of the various isolates in relation to one another, to the Du422 and Du151 Tat clones selected and to the South African consensus sequence for the Tat protein and is based on a pairwise comparison of the Tat proteins of the isolates;

FIG. 29 shows the percentage amino acid sequence identity of the sequenced Nef proteins of the various isolates in relation to one another, to the Du151 Nef clone selected and to the South African consensus sequence for the Nef protein and is based on a pairwise comparison of the Nef protein of the isolates;

FIG. 30 shows the percentage amino acid sequence identity of the sequenced Rev proteins of the various isolates in relation to one another, to the Du422 Rev clone selected and to the South African consensus sequence for the Rev protein and is based on a pairwise comparison of the Rev proteins of the isolates;

FIG. 31 shows a schematic representation of the shuffled Tat protein, including overlapping fragments for CTL epitope maintenance;

FIG. 32 a shows a nucleic acid sequence of GrttnC made up of gag (Du422), RT (Du151), shuffled tat (SEQ I.D. No. 10) and truncated nef (SEQ I.D. No. 13) (SEQ I.D. No. 29);

FIG. 32 b shows an amino acid sequence of GrttnC, made up of gag (Du422), RT (Du151), shuffled tat and truncated nef (SEQ I.D. No. 16) (SEQ I.D. No. 30);

FIG. 33 shows a plasmid map of pTHgrttnC, the DNA vaccine vector expressing GrttnC for prophylactic or therapeutic use against HIV infection;

FIG. 34 shows the Du422 gag nucleotide sequence which forms part of grttnC (SEQ I.D. No: 31);

FIG. 35 shows the Du422 Gag amino acid sequence which forms part of grttnC (SEQ I.D. No: 32);

FIG. 36 shows the Du151 reverse transcriptase (RT) nucleotide sequence which forms part of grttnC (SEQ I.D. No: 33); and

FIG. 37 shows the Du151 reverse transcriptase (RT) amino acid sequence which forms part of grttnC (SEQ I.D. No: 34).

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the selection of HIV-1 subtype C isolate regulatory and accessory genes and the use of these genes and modifications and derivatives thereof in making prophylactic and therapeutic pharmaceutical compositions and formulations, and in particular vaccines against HIV-1 subtype C. The compositions could therefore be used either prophylactically to prevent infection or therapeutically to prevent or modify disease. A number of factors must be taken into consideration in the development of an HIV vaccine and one aspect of the present invention relates to a process for the selection of suitable HIV isolates accessory and regulatory genes that may be used in the development of a vaccine.

The applicant envisages that the vaccine developed according to the above method could be used against one or more HIV subtypes as well as HIV-1 subtype C.

A process was developed to identify appropriate strains for use in developing a vaccine for HIV-1 subtype C. Viral isolates from acutely infected individuals were collected. They were sequenced in the tat, rev and nef regions and the amino acid sequences for the tat, rev and nef genes from these isolates were compared. A consensus sequence, the South African consensus sequence, was then formed by selecting the most frequently appearing amino acid at each position. The consensus sequence for each of the tat, rev and nef genes of HIV-1 subtype C also forms an aspect of the invention. Appropriate strains for vaccine development were then selected from these isolates by comparing them with the consensus sequence and characterising them phenotypically. The isolates also form an aspect of the invention.

In order to select for NSI strains which use the CCR5 co-receptor, a well established sex worker cohort was used to identify the appropriate strains. Appropriate strains were identified from acutely infected individuals by comparing them with the consensus sequence which had been formed. Viral isolates from 12 acutely infected individuals were sequenced in the tat, rev and/or nef regions and phenotypically characterised. These sequences were compared with viral isolates from 15 asymptomatic individuals from another region having more than 500 CD4 cells, as well as 11 viral isolates from AIDS patients attending a TB infectious disease hospital in Gauteng (n=9) and two children with AIDS (n=2). Other published subtype C sequences located in the Los Alamos Database were also included (http://ww.hiv-web.lanl.gov/).

Two potential vaccine strains, designated Du422 and Du151 were selected. Du422 and Du151 were selected based on amino acid homology to the consensus sequence in all three gene regions: tat, rev and net, CCR5 tropism and ability to grow and replicate in tissue culture. The nucleotide and amino acid sequences of the three gene regions of the three isolates and modifications and derivatives thereof also form aspects of the invention.

The isolation and selection of viral strains for the design of a vaccine The following criteria were used to select appropriate strains for inclusion into HIV-1 vaccines for Southern Africa:

-   -   that the strains be genotypically representative of circulating         strains;     -   that the strain not be an outlier strain;     -   that the strain be as close as possible to the consensus amino         acid sequence developed according to the invention for the tat,         rev and nef genes of HIV-1 subtype C;     -   that the strain have an R5 phenotype, i.e. a phenotype         associated with transmission for selection; and     -   that the vaccine be able to be grown in tissue culture.

The following procedure was followed in the selection of viral strains for the design of a vaccine. A well-established sex worker cohort in Kwazulu Natal, South Africa was used to identify the appropriate strains for use in an HIV vaccine. Viral isolates from 12 acutely infected individuals were sequenced in tat, rev and nef and were also isolated and phenotypically characterised. These sequences were compared with a similar collection from asymptomatc and AIDS infected (nef region) individuals from the Gauteng region in South Africa and Cape Town region of the Western Cape as well as other published subtype C sequences.

Patients

Individuals with HIV infection were recruited from 4 regions in South Africa. Blood samples were obtained from recently infected sex workers from Kwazulu-Natal (n=12). Recent infection was defined as individuals who were previously seronegative and had became seropositive within the previous year. Samples were also collected from individuals attending out-patients clinics in Cape Town (n=2), women attending antenatal clinics in Johannesburg (n=6) and men attending a STD clinic on a gold mine outside. Johannesburg (n=7). The latter 2 groups were clinically stable and were classified as asymptomatic infections. In addition, for comparison in the nef gene, 11 isolates from AIDS patients were included from Gauteng; 9 isolates from patients attending a TB infectious disease hospital and 2 isolates from children infected with AIDS. Blood samples were collected in EDTA and used to determine the CD4 T cell count and genetic analysis of the virus. In the case of recent infections a branched chain (bDNA) assay (Chiron) to measure plasma viral load was done, and the virus was isolated. HIV-1 serostatus was determined by ELISA. The results of the CD4 T cell counts and the viral loads on the sex workers were established and information on the clinical status as at date of seroconversion, CD4, and data on the co-receptor usage is set out in Table 1 below.

Virus Isolation

HIV was isolated from peripheral blood mononuclear cells (PBMC) using standard co-culture techniques with mitogen-activated donor PBMC. 2×10⁶ patient PBMC were co-cultured with 2×10⁶ donor PBMC in 12 well plates with 2 ml RPMI 1640 with 20% FCS, antibiotics and 5% IL-2 (Boehringer). Cultures were replenished twice weekly with fresh medium containing IL-2 and once with 5×10⁵/ml donor PBMC. Virus growth was monitored weekly using a commercial p24 antigen assay (Coulter). Antigen positive cultures were expanded and cultured for a further 2 weeks to obtain 40 ml of virus containing supernatant which was stored at −70° C. until use. The results of the isolation of the viruses from the commercial sex workers is also shown in Table 1 below.

Viral Phenotypes

Virus-containing supernatant was used to assess the biological phenotype of viral isolates on MT-2 and co-receptor transfected cell lines. For the MT-2 assay, 500 μl of supernatant was incubated with 5×10⁴ MT-2 cells in PRMI plus 10% FCS and antibiotics. Cultures were monitored daily for syncitia formation over 6 days. U87.CD4 cell expressing either the CCR5 or CXCR4 co-receptor were grown in DMEM with 10% FCS, antibiotics, 500 μg/ml G418 and 1 μg/ml puromycin. GHOST cells expressing minor co-receptors were grown in DMEM with 10% FCS, 500 μg/ml G418, 1 μg/ml puromycin and 100 μg/ml hygromycin. Cell lines were passaged twice weekly by trypsination. Co-receptor assays were done in 12 well plates; 5×10⁴ cells were plated in each well and allowed to adhere overnight. The following day 500 μl of virus containing supernatant was added and incubated overnight to allow viral attachment and infection and washed three times the following day. Cultures were monitored on days 4, 8 and 12 for syncitia formation and p24 antigen production. Cultures that showed evidence of syncitia and increasing concentrations of p24 antigen were considered positive for viral growth. The results of co-receptor usage of the viruses from the commercial sex workers are also shown in Table 1. TABLE 1 COHORT OF ACUTE INFECTIONS FOR SELECTION OF VACCINE CANDIDATES Duration of Co-culture p24 Sample ID Sero date Sample date infection CD4 count Viral load pos MT-2 assay Biotype Du123 17 Aug. 1998 17 Nov. 1998    3 mon 841    19,331 d6 (50 pg) NSI R5 Du151 12 Oct. 1998 24 Nov. 1998  1.5 mon 367 >500,000 d6 (>1 ng) NSI R5 Du156 16 Nov. 1998 17 Nov. 1998  <1 mon 404    22,122 d6 (>1 ng) NSI R5 Du179 13 Aug. 1997 20 May 1999   21 mon 394*    1,359* d7 (<50 pg) NSI R5 × 4 Du204 20 May. 1998 20 May 1999    1 year 633*    8,734* d7 (<50 pg) NSI R5 Du258  3 Jun. 1998 22 Jun. 1999    1 year 433*    9,114* — No isolate — Du281 24 Jul. 1998 17 Nov. 1998    4 mon 594    24,689 d6 (1 ng) NSI R5 Du285  2 Oct. 1998 — — 560*     161* — No isolate — Du368  8 Apr. 1998 24 Nov.1998  7.5 mon 670    13,993 d6 (300 pg) NSI R5 Du422  2 Oct. 1998 28 Jan. 1999    4 mon 397    17,118* d6 (600 pg) NSI R5 Du457 17 Aug. 1998 17 Nov. 1998    3 mon 665    6,658 — No isolate — Du467 26 Aug. 1998 — — 671    19,268 — No isolate — *date from November 1998 Sequencing

RNA was isolated from plasma and the gene fragments were amplified from RNA using reverse transcriptase to generate a cDNA followed by PCR to generate amplified DNA segments. The positions of the PCR primers are as follows, (numbering using the HIV-1 HXBr sequence): tat outer forward primer (5′GGC CGC AGA GGG AAC CAT AC3′ (SEQ ID No: 21) 5584-5703 bp), or rev outer reverse primer (5′GCC CTG TCT TAT TCT TCT AGG3′ (SEQ ID No: 22) 8753-8774 bp). The remaining primers used for nested PCR were as follows: the tat outer reverse primer (5′CCT CAA TAT CCC CAT CAC TCT C3′ (SEQ ID No: 23) 6226-6248 bp), tat inner forward (5′TGC CAG CAT AGC AGA ATA GG3′ (SEQ ID No: 24) 5785-5804 bp) and reverse (5′CTA TCA ATG CTC CTA CTC CTA ATC3′ (SEQ ID No: 25) 6078-6101 bp) primers and for rev, with the rev outer forward primer (5′GAT AGT AGG AGG CTT GAT AGG3′ (SEQ ID No: 26) 8285-8302 bp) and inner forward (5′GGT GTA CTC GCT ATA GTG3′ (SEQ ID No: 27) 8321-8339 bp) and reverse primers (5′CCT TCA GCT ACT GCT ATT GC3′ (SEQ ID No: 28) 8689-8698 bp).

The amplified DNA fragments were purified using the QIAQUICK PCR Purification Kit (Qiagen, Germany). The DNA fragments were then sequenced using the upstream PCR primers as sequencing primers. Sequencing was done using the Sanger dideoxyterminator strategy with fluorescent dyes attached to the dideoxynucleotides. The sequence determination was made by electrophoresis using an ABI 377 Sequencer. A mapped illustration of an HIV-1 proviral genome showing the tat, rev and nef genes sequenced as described above, is shown in FIG. 18.

Genotypic Characterisation

To select the vaccine isolate or isolates, a survey covering the three HIV genes tat (101 codons, 306 bases), rev (107 contiguous codons, 324 bases) and nef (207 codons, 618 bases) was done (FIG. 18). The map of FIG. 18 shows the 5′ long terminal repeat, the structural and functional genes (gag, pol and env) as well as the regulatory and accessory proteins (vif, tat, rev, nef, vpr and vpu). The gag open reading frame illustrates the regions encoding p17 matrix protein and the p24 core protein and the p7 and p6 nuclearcapsid proteins. The pol open reading frame illustrates the protease (PR) p15, reverse transcriptase (RT) p66 and the Rnase H integrase p51. The env open reading frame indicates the region coding for gp120 and the region coding for gp41.

Of a total of 38 isolates, 12 were from the Durban cohort (DU), 24 were from Johannesburg (GG, RB, COT and SW) and 2 from Cape Town (CT). Of these 17 were sequenced in the tat gene, 17 in the rev gene and 32 in the nef gene. The isolates that were sequenced are shown in Table 2. TABLE 2 LIST OF ISOLATES AND THE REGIONS GENES SEQUENCED Isolate Tat sequence Rev sequence Nef sequence CTSC1 ✓ — — CTSC2 ✓ ✓ ✓ Du123 ✓ ✓ ✓ Du151 ✓ ✓ ✓ Du156 ✓ ✓ — Du179 ✓ ✓ ✓ Du204 ✓ ✓ — Du258 — — ✓ Du281 ✓ ✓ — Du368 ✓ ✓ ✓ Du422 ✓ ✓ ✓ Du457 — — ✓ Du467 — — ✓ GG10 ✓ ✓ ✓ GG2 ✓ — ✓ GG3 — — ✓ GG4 ✓ — ✓ GG5 — ✓ ✓ GG6 — — ✓ RB12 ✓ ✓ ✓ RB13 ✓ ✓ ✓ RB15 — — ✓ RB18 — ✓ ✓ RB21 — ✓ ✓ RB27 — ✓ — RB28 ✓ ✓ ✓ SW10 — — ✓ SW7 — — ✓ SW15 — — ✓ SW5 — — ✓ SW20 — — ✓ SW9 — — ✓ SW2 — — ✓ SW8 — — ✓ SW23 — — ✓ COT2 — — ✓ COT6 — — ✓

The nucleic acid sequences from the Durban (Du) Johannesburg (GG, RB, SW and COT) and Cape Town (CT) cohorts were phylogenetically compared to a number of available published subtype C sequences (obtained from the Los Alamos HIV Sequence Database) including sequences from the other southern African countries and the overall subtype C consensus from the Los Alamos HIV sequence database. This comparison was done to ensure that the selected vaccine isolates were not phylogenetic outliers when compared to the Southern African sequences and the results of the comparison are shown in FIG. 19, FIG. 20 and FIG. 21. FIGS. 19 to 21 illustrate that the sequences from Southern Africa are divergent and that the Indian sequences usually form a separate distinct cluster from these African sequences. The South African sequences are not unique and, in general, are as related to each other as they are to other sequences from Southern Africa. Overall this suggests Indian sequences are unique from Southern African subtype C sequences and that we do not have a clonal epidemic in South Africa, but rather South African viruses reflect the diversity of subtype C viruses in the Southern African region

Determination of a Consensus Sequence

Amino acid sequences were derived from the sequences shown in Table 2 and were used to determine a South African consensus sequence. The most frequently appearing amino acid at each position was selected as the consensus amino acid at that position. In this way, the consensus sequence was determined along the linear length of each of the sequenced genes (tat, rev and nef genes). The alignments were done using the DNAMAN program (DNAMAN2 output), which generates a consensus sequence in this manner. These resulted in the consensus sequence for each gene region. The alignments of the amino acid sequences and the resulting consensus sequences are shown in FIGS. 22, 23 and 24. The amino acid similarities are shown in FIGS. 25 to 27.

The final choice of which isolate or isolates to use was based on the similarity of the sequence of the tat, rev and nef genes of a particular isolate to the South African consensus sequence that had been derived as set out above, as well as the availability of an R5 isolate which had good replication kinetics as shown in Table 1.

Selection of Vaccine Isolates

Based on the considerations and methodology set out above, two strains were selected from the acute infection cohort as the vaccine strains. The first strain is Du151 for the tat and nef genes and the second strain is Du422 for the tat and rev genes. These three strains were selected for the following reasons:

-   -   1. At the time the samples were obtained, Du151 had been         infected for 6 weeks and had a CD4 count of 367 cells per ul of         blood and a viral load above 500,000 copies per ml of plasma.         Given the high viral load, and the recorded time from infection,         it is probable that the individual was still in the initial         stages of viraemia prior to control of HIV replication by the         immune system.     -   2. At the time the samples were obtained, Du422 had been         infected for 4 months with a CD4 count of 397 cells per ul of         blood and a viral load of 17,118 copies per ml of plasma. In         contrast to Du151, this individual had already brought viral         replication under control to a certain extent.

Both isolates are able to grow in cell culture and have been sequence analyzed throughout their whole genome.

Based on the analysis of the amino acid pairwise comparison between Du151 and Du422 Tat protein sequences and other isolates shown in FIG. 28, the Du151 and Du422 tat sequences were shown to be very similar to the South African consensus sequence shown in FIGS. 19 and 22. They shared 89.4% (Du151) and 91.6% (Du422) amino acid sequence identity with the consensus sequence. Both Du151 and Du422 were thus used to generate the resynthesized, shuffled Tat in both a wild-type (non-codon optimized) and humanized (codon-optimized) form. They were chosen over slightly closer related isolates to the South African consensus sequence due to their ability to grow in tissue culture and due to both isolates entire genome having been sequenced and characterized.

The nef gene showed the greatest sequence diversity. Based on the analysis of the Nef amino acid pairwise identity score with the SA consensus (93.4%) shown in FIG. 29, we chose the Du151 isolate as the source of the nef gene. All pairwise identity scores are above 80.2% with either the Du151 isolate sequence when compared to the other recent seroconverters, as shown in FIG. 29. Other contributing factors in this decision were that this is the same isolate that was chosen for the source of the env and pot genes and that this was an isolate with excellent growth properties in vitro.

The rev gene was the most conserved of the three. Based on the amino acid pairwise identity score with the SA consensus (95.2%), the Du422 rev gene was selected. In addition, all pairwise identity scores are above 83% with the Du422 isolate sequence when compared to the other recent seroconverters, as shown in FIG. 30. These pairwise scores make the Du422 sequence similar to the best scores in this sequence pool and combine these levels of similarity with an R5 virus with good cell culture replication kinetics.

Resynthesis of Genes

The Tat-nef polyprotein gene was produced by synthesis of oligonucleotide fragments that were ligated together to form the full gene by GeneArt (geneart GmbH, Regensburg). The codon optimised and non-codon optimised versions were synthesised and cloned into pPCR-Script (Stratagene) vector. The identity of the insert was confirmed by sequencing the insert on both strands and comparing these sequences to the original sequences. The modifications to the tat and nef gene sequences of Du422/Du151 and Du151 separately and Tat-nef polyprotein gene sequence are shown in Sequence I.D. Nos. 9-17.

The Tat protein was split into three overlapping fragments and reshuffled (as shown in FIG. 31) to inactivate the protein, making it safer, but without losing potential CTL epitopes. The Nef protein was shortened by 10 amino acids, removing the N terminal myristylation site that allows the Nef protein to exit the cell (SEQ I.D. No.12). Apart from making the protein safer, it is hoped that this will result in a more efficient CTL response, as the protein is trapped inside the cell.

Vaccine Development

The vaccines of the invention will be formulated in a number of different ways using a variety of different vectors. They involve encapsulating RNA or transcribed DNA sequences from the viruses in a variety of different vectors. The vaccines may contain at least part of the tat and rev genes from the Du422 isolate, and at least part of the tat and nef genes from the Du151 isolate of the present invention or derivatives or modifications thereof.

Genes for use in DNA vaccines have been resynthesized to reflect human codon usage. The tat Du422 gene was also divided into three fragments with overlapping ends so that no potential CTL epitopes are lost and reshuffled to improve safety of the Tat protein. The Du151 nef gene had the first 10 amino acids deleted to remove the myristylation site for safety reasons. The reshuffled tat and shortened nef were then synthesised together in the same reading frame to constitute a Tat-Nef polyprotein. Both humanised and non-humanised versions of the Tat-nef polyprotein have been synthesised for alternative vaccines. A similarly codon optimised rev gene may be expressed by DNA vaccines.

Other vaccines will contain DNA transcribed from the RNA for the tat gene from the Du422 and Du151 isolates, DNA transcribed from the RNA for the nef gene from the Du151 isolate and DNA transcribed from the RNA for the rev gene from the Du422 isolate. These genes could also be expressed as oligomeric envelope glycoprotein complexes (Progenics, USA) as published in J Virol 2000 January; 74(2):627-43 (Binley, J. L. et al.), or in the adeno associated virus (AAV) (Target Genetics), the Venezuelan equine encephalitus virus (U.S. patent application Ser. No. 60/216,995, which is incorporated herein by reference) as well as in Modified Vaccinia Ankara (MVA) (Amara et al., 2002), BCG and other vaccines being developed at the University of Cape Town.

A vaccine construct containing an in frame polygene, GrttnC (FIGS. 32 a and 32 b; SEQ I.D. Nos. 29 and 30) including codon optimised Du422 gag (FIGS. 34 and 35; SEQ I.D. Nos. 31 and 32), Du151 RT (reverse transcriptase) (FIGS. 36 and 37; SEQ I.D. Nos. 33 and 34) (WO 02/04494, the contents of which are incorporated herein by reference) and the shuffled tat—truncated nef (SEQ I.D. No. 17) has been developed and will be incorporated into a number of vaccine candidates, including a DNA vaccine, pTHgrttnC (FIG. 33) using the pTH DNA vaccine vector (Hanke et al., 2000) and an MVA vaccine (Amara at al., 2002). The nucleotide and amino acid sequences of the gag and pol genes isolated from Du422 and Du151 are shown in SEQ I.D. Nos. 35 to 38, respectively.

The invention is not intended to be limited to the precise embodiments described.

Deposits

The following material has been deposited with the European Collection of Cell Cultures, Centre for Applied Microbiology and Research, Salisbury, Wiltshire SP4 OJG, United Kingdom (ECACC). Material ECACC Deposit No. Deposit Date HIV-1 Viral isolate Du151 Accession Number 27 Jul. 2000 00072724 HIV-1 Viral isolate Du422 Provisional Accession 27 Jul. 2000 Number 00072726 Provisional Accession 22 Mar. 2001 Number 01032114

The deposit was made under the provisions of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure and regulations thereunder (Budapest Treaty).

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1-29. (canceled)
 30. Use of at least one shuffled tat sequence and/or at least one truncated nef sequence in the manufacture of a vaccine for use in the treatment or prevention of HIV infection, wherein the tat sequence is: a sequence set out in any one of FIGS. 9-11; or a sequence which is a modified derivative of the sequence of any one of FIGS. 1-4, wherein the modification is a result of shuffling of the sequence of any one of FIGS. 1-4; and wherein the nef sequence is: a sequence set out in any one of FIGS. 12-14 (SEQ I.D. Nos. 12-14); or a sequence which is a modified derivative of the sequence of either one of FIGS. 5 and 6 (SEQ I.D. Nos. 5 and 6), wherein the modification is a result of truncation of the sequence of either one of FIGS. 5 and
 6. 31. Use according to claim 30, wherein the vaccine comprises a shuffled tat sequence and a truncated nef sequence, the combined sequence being: (i) a sequence set out in any one of FIGS. 15 to 17 (SEQ I.D. Nos. 15 to 17); (ii) a sequence which is at least 90% similar to the amino acid sequence of FIG. 16 (SEQ I.D. No. 16) and which has substantially similar immunogenicity; or (iii) a sequence which is a modified derivative of the amino acid sequence set out in FIG. 16, wherein the modification is a shuffling or truncation.
 32. Use according to claim 30, wherein the shuffled tat sequence is a sequence selected from any one of FIGS. 9-11 (SEQ I.D. Nos. 9-11) and/or the truncated nef sequence is a sequence set out in any one of FIGS. 12-14 (SEQ I.D. Nos. 12-14).
 33. A vaccine for the treatment or prevention of HIV infection comprising at least one shuffled tat sequence set out in any one of FIGS. 9-11 (SEQ I.D. Nos. 9-11) and/or at least one truncated nef sequence set out in any one of FIGS. 12-14 (SEQ I.D. Nos. 12-14).
 34. A vaccine according to claim 33, comprising at least portions of a gag gene sequence, a reverse transcriptase (pol) gene sequence, a shuffled tat gene sequence and a truncated nef gene sequence which have been ligated to form an in frame polygene designated grttnC (SEQ I.D. Nos: 29 or 30).
 35. A molecule comprising: (i) the nucleotide sequence set out in FIG. 15 (SEQ I.D. No. 15) or FIG. 17 (SEQ I.D. No. 17); (ii) an RNA sequence corresponding to the nucleotide sequence set out in FIG. 15 (SEQ I.D. No. 15) or FIG. 17 (SEQ I.D. No. 17); (iii) a sequence which is at least 90% or greater DNA similar to the nucleotide sequence set out in FIG. 15 (SEQ I.D. No. 15) or FIG. 17 (SEQ I.D. No. 17), or an RNA sequence corresponding to these sequences, and which displays substantially similar immunogenicity; or (iv) a sequence which is a modified derivative of the sequence of any one of (i) to (iii), wherein the modification is a shuffling or truncation.
 36. A polypeptide comprising: (i) the amino acid sequence set out in FIG. 16 (SEQ I.D. No. 16); (ii) an amino acid sequence which is at least 90% similar to the sequence of FIG. 16 and which has substantially similar immunogenicity; or (iii) a sequence which is a modified derivative of the amino acid sequence set out in FIG. 16 (SEQ I.D. No. 16), wherein the modification is a result of shuffling or truncation.
 37. A molecule comprising: (i) the nucleotide sequence as set out in FIG. 1 (SEQ I.D. No. 1) or FIG. 3 (SEQ I.D. No. 3); (ii) an RNA sequence corresponding to the nucleotide sequence set out in FIG. 1 (SEQ I.D. No. 1) or FIG. 3 (SEQ I.D. No. 3); (iii) a sequence which is at least 97% DNA similar to the nucleotide sequence set out in FIG. 1 (SEQ I.D. No. 1) or FIG. 3 (SEQ I.D. No. 3), or an RNA sequence corresponding to these sequences, and which displays substantially similar immunogenicity; (iv) a sequence which is a modified derivative of the sequence of any one of (i) to (iii), wherein the modification is a result of shuffling.
 38. A molecule according to claim 37, wherein the modified sequence is a tat sequence set out in either one of FIGS. 9 and 10 (SEQ I.D. No. 9 and No. 10) which has been shuffled so as to inactivate the protein encoded by the molecule while maintaining CTL epitopes.
 39. A polypeptide comprising: (i) the amino acid sequence set out in either one of FIG. 2 (SEQ I.D. No. 2) or FIG. 4 (SEQ I.D. No. 4); (ii) a sequence which is at least 95% similar to the sequence of FIG. 2 (SEQ I.D. No. 2) or FIG. 4 (SEQ I.D. No. 4) and which has substantially similar immunogenicity; or (iii) a sequence which is a modified derivative of the amino acid sequence set out in FIG. 2 (SEQ I.D. No. 2) or FIG. 4 (SEQ I.D. No. 4), wherein the modification is a result of shuffling of the nucleotide sequence encoding the polypeptide.
 40. A polypeptide according to claim 39, wherein the modified sequence is a shuffled Tat sequence set out in FIG. 11 (SEQ I.D. No. 11).
 41. A molecule comprising: (i) the nucleotide sequence set out in FIG. 5 (SEQ I.D. No. 5); (ii) an RNA sequence corresponding to the nucleotide sequence set out in FIG. 5 (SEQ I.D. No. 5); (iii) a sequence which is at least 98% DNA similar to the nucleotide sequence set out in FIG. 5 (SEQ I.D. No. 5) or an RNA sequence corresponding to it, and which displays substantially similar immunogenicity; or (iv) a sequence which is a modified derivative of the sequence of any one of (i) to (iii), wherein the modification is a truncation.
 42. A molecule according to claim 41, wherein the modified sequence is a truncated nef sequence set out in either one of FIGS. 12 and 13 (SEQ I.D. Nos. 12 and 13).
 43. A polypeptide comprising: (i) the amino acid sequence set out in FIG. 6 (SEQ I.D. No. 6); (ii) a sequence which is at least 92% similar to the sequence of FIG. 6 and which has substantially similar immunogenicity; or (iii) a sequence which is a modified derivative of the amino acid sequence set out in FIG. 6 (SEQ I.D. No. 6), wherein the modification is a result of a truncation of the nucleotide sequence encoding the polypeptide.
 44. A polypeptide according to claim 43, wherein the modified sequence is a truncated Nef sequence set out in FIG. 14 (SEQ I.D. No. 14). 